Re3Ga5O12塊材與Ba(Mg1/3Ta2/3)O3薄膜之光譜性質研究

Abstract

我們研究不同稀土元素取代之 Re3Ga5O12 (Re = Nd, Sm, Eu, and Dy) 塊材以及不同成長條件之 Ba(Mg1/3Ta2/3)O3 薄膜的光譜性質，並 探討紅外光譜特徵與其微波特性的關連。 首先，我們觀察到 (i) Re3Ga5O12 塊材具有 14 個遠外紅光區聲子 振動，並推算出離子晶格貢獻的介電常數與品質因子；(ii) 在 200 cm-1 ~ 800 cm-1 的鎵四面體的內膜振動聲子決定了大部份的介電特性，隨 著鑭系收縮效應聲子振動頻率呈現合理的藍移，其中介電貢獻第一、 二名的 9、10 號聲子 (同為鎵四面體非對稱彎曲振動模)，其半高寬 趨勢與微波量測所得的品質因子趨勢呈高度負相關，可說 Re3Ga5O12 塊材複雜的結構中鎵四面體主導了其主要的介電性質。 再者，我們觀察到 (i) Ba(Mg1/3Ta2/3)O3 薄膜巨觀排列屬於無序的 立方晶系結構 ( Pm3m )，微細結構則介於無序立方晶系及有序六角 晶系結構 ( P3m1) 間的過渡態，此外隨著鍍膜時間的增加，我們發現 到 BaCO3 雜相的生成，這影響了Ba(Mg1/3Ta2/3)O3 薄膜品質；(ii) 利 用紅外光光譜推算薄膜的介電特性，薄膜靜介電常數最高可達到 13.27，與塊材 (約 25) 有段距離，而品質因子最好僅為 9980 GHz， 與塊材 (約 70000 GHz) 相距甚遠。We study the optical properties of Re3Ga5O12 (Re = Nd, Sm, Eu, and Dy) bulk and Ba(Mg1/3Ta2/3)O3 films with different preparation conditions. And we discuss the correlation between their infrared characteristics and microwave properties. First, we obtain the following results. (i) Re3Ga5O12 bulk has fourteen infrared phonons and we calcaulate the dielectric constant and Q×f factor which are contributed by ionic lattice. (ii) The internal mode phonons of the GaO4 tetrahedron within 200 cm-1 ~ 800 cm-1 decide the most part of dielectric properties. With the Lanthanide contraction effect, the phonons exhibit blue shift for their vibration frequency. The linewidths of No.9 and No.10 phonons, which are GaO4 asymmetric bending mode have highly negative correlation with quality factor. We can say the GaO4 tetrahedron leads main dielectric characteristics among the complex structure of Re3Ga5O12. Moreover, we find the following results. (i) The macroscopic arrangement of the Ba(Mg1/3Ta2/3)O3 films belong to disordered cubic system and the microstructure of the films shows a transition-state between disordered cubic and ordered hexagonal system. Besides, we observe the growth of secondary phase (BaCO3 phase) with the increasement of depositon time. (ii) The biggest static dielectric constant of the Ba(Mg1/3Ta2/3)O3 film determined from the far-infrared spectra is 13.27, smaller than the value of 25 in bulk materials. However, the biggest quality factor Q × f at 1 THz is 9880 GHz, which is markedly smaller than that of bulk about 70000 GHz.